"Experimental measurement of elastic moduli in the moss Physcomitrium patens informs modeling of plant cell tip growth"
Plant cell morphology and growth are essential for plant development and adaptation. Some key cell types, such as pollen tubes, root hairs, and moss protonemata, develop specifically by tip growth. Cell wall material deposition and internal structure rearrangement (wall loosening) are the major contributing factors to the growth and morphogenesis of tip cells. As the cell wall is physically extended due to turgor pressure, we must understand the wall mechanical response against turgor pressure in order to elucidate this complex process. Studies into this process include theoretical modeling of tip growing cells, which are mostly based on the classical Lockhart theory, where the wall extends irreversibly in response to turgor pressure. These models predict that the shape of growing cells is critically dependent on a dramatic gradient of elastic moduli or effective viscosities from the tip domain to the shank region. While the elastic moduli have been measured experimentally in yeast and other tip-growing cells in simplified settings, the dramatic gradient transcending a difference in the order of several magnitudes has never been found. We argue the previous prediction is biased because these models do not distinguish wall deformation due to active processes, such as wall material deposition and wall loosening, from its elastic properties. Our research attempts to address these concerns by first measuring elastic moduli using our model organism, the moss Physcomitrium patens. We use a novel technique of measuring the elastic property by quantifying wall deformation from fluorescent bead tracking and surface region triangulation; and quantifying the wall tension from wall surface shape analysis. We find that there does exist a gradient of moduli between the tip and shank, but with a difference within an order of magnitude. Additional samples and improvement of error analysis will allow us to confirm this and investigate further into differences between cell types in P. patens. We will then apply this technique on other experiments to study how these elastic moduli differ during growth, or when cell wall composition is modified. This novel method will help bring advancements to the field of cell wall mechanics and the understanding of tip cell growth.
Additional authors: Luis Vidali (1,2); Min Wu (1,3) (1) Bioinformatics and Computational Biology, Worcester Polytechnic Institute, Worcester, 01609, MA, USA (2) Biology and Biotechnology, Worcester Polytechnic Institute, Worcester, 01609, MA, USA (3) Mathematical Sciences, Worcester Polytechnic Institute, Worcester, 01609, MA, USA